How much should I pay someone to go investigate a property?

My suggestion would be to start investigating the type of investing you want to do and really deep dive into that topic.

I am investigating many solo 401k providers or custodians but am very hesitant because I am Wondering what happens if the custodian runs off with my money?

Upon my further investigation I notice that whoever did the renovation tried to hide the damage instead of fixing it! 

You're going to have ten years of looking over your shoulder because what you've done will be patently obvious to any investigator.

I still need to investigate further.

Different property types have different % rules of thumb for preliminary estimating, but lenders and investors will require details.Using the 50% rule as a starting point the 50% Rule Cash Flow Estimates Post-Refinance calculation shows negative cash-flow, but the analysis over time does not reflect that? 

A lot of real estate investors have connections with title companies or lawyers who can run preliminary title searches on properties during the due diligence process.

In California, a 30 day feasibility (aka due diligence aka investigation period aka option period) is pretty rare; they usually need 45 days or 60 days, or even 90 days if they need enough time to assess the viability of a re-zone, general plan amendment, or if there are complicated soils or enviromental issues. 

A property that shares a wall with another property where the 2nd property has a door to the roof of the property for sell (could require a drone to see).As the auction nears, the normal houses get removed as the owner gets current on their taxes.As the auction is a couple days away, I use my contacts to run preliminary title checks on a few of the best candidates remaining (I do not want to abuse the relationship).